Ventilator Induced Lung Injury (VILI) is a common cause of morbidity and sometimes mortality in critically ill patients with respiratory failure. The types of VILI include barotraumas, volutrauma, atelectrauma, and biotrauma. Thus ventilator setting is a delicate balance between achieving sufficient ventilation but avoiding excessive pressure and overdistension or too little pressure and excessive shear stress when ventilatory units cycle between open and closed. In addition, critically ill patients most often cannot be moved to a CT scanner, which is the traditional method for evaluating adequate ventilation. Thus in order to optimally adjust ventilator settings in an ICU, there is a need for a noninvasive, relatively portable device that can measure regional ventilation. To address this need, in this application, we propose building a portable ventilation stethoscope (VS). The Ventilation Stethoscope is a portable device designed to measure quantitative regional ventilation using the same principles as in Magnetic Resonance Imaging (MRI). Unlike the traditional MRI system, the device is portable, smaller, and performs a measurement of regional ventilation with a single probe (similar to a stethoscope). Thus the VS is a low field (~0.01T) magnetic resonance spectrometer. To enhance sensitivity hyperpolarized 129Xe gas will be injected into the ventilator output. A key aspect of this proposal is the development of a portable continuous flow xenon laser polarizer to produce a steady source of hyperpolarized 129Xe gas. The VS probe will consist of permanent magnets integrated with the rf coil into a single planar structure such that it has a region of magnetic field homogeneity external to the structure itself that is projectd into the lung at a known depth. With this device, we propose to demonstrate the measurement of regional ventilation in healthy adult human volunteers.